The role of hydromechanical coupling in fractured rock engineering

Abstract

This paper provides a review of hydromechanical (HM) couplings in fractured rock, with special emphasis on HM interactions as a result of, or directly connected with human activities. In the early 1960s, the coupling between hydraulic and mechanical processes in fractured rock started to receive wide attention. A series of events including dam failures, landslides, and injection-induced earthquakes were believed to result from HM interaction. Moreover, the advent of the computer technology in the 1970s made possible the integration of nonlinear processes such as stress–permeability coupling and rock mass failure into coupled HM analysis. Coupled HM analysis is currently being applied to many geological engineering practices. One key parameter in such analyses is a good estimate of the relationship between stress and permeability. Based on available laboratory and field data, it was found that the permeability of fractured rock masses tends to be most sensitive to stress changes at shallow depth (low stress) and in areas of low in-situ permeability. In highly permeable, fractured rock sections, fluid flow may take place in clusters of connected fractures which are locked open as a result of previous shear dislocation or partial cementation of hard mineral filling. Such locked-open fractures tend to be relatively insensitive to stress and may therefore be conductive at great depths. Because of the great variability of HM properties in fractured rock, and the difficulties in using laboratory data for deriving in-situ material properties, the HM properties of fractured rock masses are best characterized in situ.

Notes

Acknowledgements

Technical review and comments by Dr. Christopher E. Neuzil, US Geological Survey, Dr. Chin-Fu Tsang, Lawrence Berkeley National Laboratory, and Tech. Lic. Ki-Bok Min, Royal Institute of Technology, Sweden are much appreciated. The following organizations are gratefully acknowledged for their financial support: the Director, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biological Sciences, of the US Department of Energy, under contract no. DE-AC03-76-SF00098; the DECOVALEX Project through the Swedish Nuclear Power Inspectorate; and the European Commission through the BENCHPAR project under contract FIKW-CT-2000-00066.

Appendix

Abbreviations

Most symbols are defined the first time they occur. The following list contains an explanation of the symbols that need further explanation and symbols that are most frequently used. Boldface letters represent matrix or vector quantities, and scalars are shown in italic.

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